Automatic focus system calibration for image capture systems

ABSTRACT

Imaging systems and methods for calibrating imaging systems are provided. The imaging system has a body, a scene image capture system that captures images using a taking lens system that can be set to a plurality of different focus distances, and a rangefinder that is capable of determining a distance between the imaging system and at least one portion of a field of view of the taking lens system. The method comprises: automatically capturing a first calibration image of a first field of view through the taking lens system with the taking lens system set to a first focus distance setting; identifying a portion of the first calibration image having a predetermined degree of focus; using the rangefinder to determine a first calibration distance from the imaging device to the identified portion. A focus correlation is determined based upon the first calibration distance and the first focus distance setting.

FIELD OF THE INVENTION

The invention relates to automatic calibration of imaging systems toimprove image quality and enable faster operation.

BACKGROUND OF THE INVENTION

Imaging systems are limited in terms of image quality by artifactsintroduced by the environment that they are operated in. One way toavoid capturing or creating images that have such artifacts is tocalibrate the imaging system in an environment that is similar to theenvironment in which it will be used. Often this is done when theimaging device is manufactured. For example, it is known in the art touse test fixtures to calibrate autofocus systems in film cameras whilesuch cameras are within an operating range of environmental conditions.

In particular, one aspect of an imaging system that benefits fromcalibration is the autofocus system in an imaging system. Many filmcameras, digital cameras and scanners capture images using an imager anda lens system with an adjustable focus lens system. Typically, the focusdistance of such an adjustable focus lens system can automatically beset to one of a plurality of different settings by sensing, control anddrive systems that are adapted to provide optimal focus of what isdetermined to be a subject area in a scene. Lens systems that haveautomatically adjustable focus settings are referred to herein asautofocus systems.

It will be appreciated that it is important to properly calibrate suchautofocus systems. In the above example, focus settings for film camerasare calibrated by using the test fixture to monitor an image provided bythe lens system of such a film camera and adjusting the lens systemuntil the lens system reaches a first setting where a test targetlocated at a first distance from the camera is in focus. The rangefinderfor the film camera is then used to measure the distance to the testtarget and thereafter the rangefinder will position the lens system atthe first setting whenever the rangefinder measures that distance. Thisprocess is then repeated for a plurality of other test targets, eachlocated at one of a range of additional distances so that therangefinding measurements are associated with each of a plurality orlens focus settings.

Digital cameras typically use one of two types of autofocus systems:rangefinder type autofocus systems or a “through-the-lens” typeautofocus system to automatically determine taking lens focus settings.A rangefinder autofocus system uses sensors such as optical rangefindersor sonic rangefinders to determine a distance from a camera to one ormore portions of a scene within a field of view of the adjustable lenssystem. Common rangefinder type autofocus systems include active andpassive systems. In one example of an active rangefinder type system,the rangefinder type autofocus system compares two low-resolution imagesthat have been captured through two lens systems that are separatedlaterally by a distance and determine the distance to the scene throughtriangulation. The focus setting of the adjustable focus lens system isthen determined using a calibrated preprogrammed curve or look-up tablethat correlates scene distances with lens positions that can be used tocapture objects at the scene distance in focus. A wide variety ofrangefinder type autofocus systems are very well known in the art.

Rangefinder type autofocus systems have the advantage of being very fastwith some having a response time that can be in the range of 0.01-0.05second. However, the focus quality produced by some rangefinder typeautofocus systems can vary when they are used in different operatingconditions. For example, temperature and humidity can affect thecalibration of the distance to focus lens position curve due tofluctuations in the refractive index and dimensions of both therangefinder autofocus system components and the taking lens components.

The “through-the-lens” autofocus system determines focus settings usinganalysis of a series of images captured with the lens system positionedat a plurality of different focus distances. For example, in a contrastbased “through-the-lens” autofocus system a plurality of differentimages (e.g. 5-20) are captured with the taking lens in different focuslens positions in a so-called hill climb method. The contrast present inthe captured images is compared and the image with the greatest contrastis determined to be the image with the best focus conditions (often thebest focus lens position is further refined by interpolating thecontrast values between images). The “through-the-lens” type autofocussystem is very accurate since it measures focus quality directly fromimages captured with the high quality taking lens.

However, conventional “through-the-lens” type autofocus systems can berelatively slow in determining a focus setting. For example, suchsystems can take as long as 0.5-2.0 seconds to determine a focusdistance. This is because such “through-the-lens” autofocus systemsrequire the capture and processing of a number of images.

Accordingly, in some digital cameras, the two types of autofocus systemsare used together in a hybrid system in which the rangefinder typeautofocus system is used to provide a fast estimation of a focus settingthat is then followed by the use of the “through-the-lens” autofocussystem to refine the focus setting. For example, U.S. Pat. No. 6,864,474entitled “Focusing Apparatus for Adjusting Focus of an OpticalInstrument”, filed by Misawa on Jan. 10, 2003, describes the coordinateduse of a rangefinder type autofocus system with a through-the-lensautofocus system. In Misawa, the focus position of the taking lens isdetermined by both the rangefinder based autofocus system and the“through-the-lens” autofocus system, the difference between the focusposition determined by the rangefinder type autofocus system and thefocus position determined by the “through-the-lens” type autofocussystem is stored for future reference. In subsequent image captureepisodes, the stored difference information is used to refine the numberof images captured and analyzed by the “through-the-lens” type autofocussystem in the hill climb method to determine the focus lens positionwith best focus, thereby reducing the number of images captured andprocessed when the rangefinder has been accurate and increasing thenumber of images captured and processed when the rangefinder has beeninaccurate. However, the method described by Misawa assumes that theperformance of the rangefinder, adjustable focus lens system, andcontrol system are consistent over time, do not fluctuate withvariations in environmental conditions and do not otherwise change ordrift over time.

Misawa also does not eliminate the use of multiple image capture andprocessing used by the “through-the-lens” type autofocus system so thatthe hybrid autofocus as described by Misawa remains slow. A furtheraspect of an imaging system that would benefit from calibration is aprojection system in order to ensure that a projection lens system isproperly focused. There have been efforts to provide automatic feedbacksystems to this end. For example, U.S. Patent Application PublicationsUS2005/0168705 and US2005/0024606 both by Li et al., describe projectionsystems which include feedback of a projected image by an imaging sensorsystem. In this case Li et al. teaches the use of the imaging sensorsystem to aid in focusing the projector. Li et al. also teaches the useof an imaging sensor system to enable the projection system to correctfor projector-to-surface orientation problems, such as correcting toadjust for keystone in the projected image, or to fit the projectedimage within the edge of a projection screen. Thus, Li et al. discloses,essentially, a “through-the-lens” focus system with orientationcompensation. However, here again calibration of such a system istypically performed only during manufacturing or during a manual serviceprocedure.

Therefore the need persists to improve imaging systems through newcalibration approaches.

SUMMARY OF THE INVENTION

Image capture systems and methods for calibrating an imaging system areprovided. In one aspect of the invention, the imaging system has a body,a scene image capture system that captures images using a taking lenssystem that can be set to a plurality of different focus distances, anda rangefinder that is capable of determining a distance between theimaging system and at least one portion of a field of view of the takinglens system. The method comprises the steps of: automatically capturinga first calibration image of a first field of view through the takinglens system with the taking lens system set to a first focus distancesetting; identifying a portion of the first calibration image having apredetermined degree of focus; using the rangefinder to determine afirst calibration distance from the imaging device to the identifiedportion of the first calibration image; determining a focus correlationbased upon the first calibration distance and the first focus distancesetting, said focus correlation associating different rangefinderdetermined distances with each of the plurality of focus distancesettings with at least one rangefinder determined distance; detecting acapture condition indicating that the scene image capture system is tobe used to capture an archival image of a scene and, in responsethereto, performing the steps of: determining a capture distance fromthe imaging system to a portion of the field of view of the taking lenssystem using the rangefinder, and setting the focus distance setting forthe taking lens system for the capture of the archival image based uponthe determined focus correlation and the determined capture distance.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments presentedbelow, reference is made to the accompanying drawings, in which:

FIG. 1 shows a block diagram of one embodiment of an image capturesystem;

FIG. 2 shows a back, elevation view of the image capture system of FIG.1;

FIG. 3 shows a front, elevation view of the image capture system of FIG.1;

FIG. 4 shows a block flow diagram of one embodiment of anauto-calibrating rangefinder-based autofocus system;

FIG. 5 illustrates one example of a calibration image;

FIG. 6 illustrates one example of a focus correlation;

FIG. 7 illustrates one example of a focus correlation;

FIG. 8 illustrates one example of a focus correlation;

FIG. 9 shows another embodiment of a method for calibrating an imagingdevice;

FIG. 10 shows another embodiment of a method for calibrating an imagingdevice;

FIG. 11 shows another embodiment of a method for calibrating an imagingdevice;

FIG. 12 shows another embodiment of a method for calibrating an imagingdevice;.

FIG. 13 shows one example of a focus correlation;

FIG. 14 shows one example of a focus correlation;

FIG. 15 shows one example of a focus correlation;

FIG. 16 shows another embodiment of a method for determining a focuscorrelation;

FIG. 17 shows an embodiment of an imaging device with an associatedprojection system; and

FIG. 18 shows a method for calibrating the projection system.

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the present embodiments in detail, it is to beunderstood that the embodiments are not limited to the particulardescriptions and that it can be practiced or carried out in variousways.

FIG. 1 shows a block diagram of an embodiment of an imaging system 10.FIG. 2 shows a back, elevation view of the imaging system 10 of FIG. 1,while FIG. 3 shows a front elevation view of the imaging system 10 ofFIG. 1. As is shown in FIGS. 1-3, imaging system 10 takes the form of adigital camera 12 comprising a body 20 to which a scene image capturesystem 22 and autofocus system 27 are mounted. Scene image capturesystem 22 having a taking lens system 23, a scene image sensor 24, asignal processor 26, an optional display driver 28 and a display 30. Inoperation, light from a scene is focused by taking lens system 23 toform an image on scene image sensor 24. Taking lens system 23 can haveone or more elements.

Taking lens system 23 is of an automatically adjustable type. In theembodiment shown in FIGS. 1-3, taking lens system 23 is automaticallyadjusted to a variety of focus settings. In the example embodiment shownin FIG. 1, taking lens system 23 is a 6× zoom lens unit in which amobile element or elements (not shown) are driven, relative to astationary element or elements (not shown) by lens driver 25 that ismotorized for automatic movement. Lens driver 25 controls both the lensfocal length and the lens focus position of taking lens system 23 andsets a lens focal length and/or position based upon signals from signalprocessor 26, an optional automatic range finder system 27, and/orcontroller 32. It will be appreciated that in other embodiments, takinglens system 23 can comprise lenses having shapes that can be changed toprovide an in situ variation of lens focus distance by modification oflens characteristics such as curvature. Examples of lens systems of thistype include those that use, for example, liquid lens technology knownto those of skill in the art. In such embodiments, lens driver 25 canprovide signals to cause focus distance changes in the lens without useof a motor. Examples of such liquid lenses include lenses soldcommercially under the name of FluidFocus by Royal Philips Electronics,Amsterdam, The Netherlands and other liquid lens products sold by PGSPrecision, Singapore.

In the embodiment of FIG. 1, the focus position of taking lens system 23can be automatically selected by a variety of known strategies. Forexample, in one embodiment, scene image sensor 24 is used to providemulti-spot autofocus using what is called the “through focus” or “wholeway scanning” approach. As described in commonly assigned U.S. Pat. No.5,877,809 entitled “Method Of Automatic Object Detection In An Image”,filed by Omata et al. on Oct. 15, 1996, the disclosure of which isherein incorporated by reference. If the target object is moving, objecttracking may be performed, as described in commonly assigned U.S. Pat.No. 6,067,114 entitled “Detecting Compositional Change in Image” filedby Omata et al. on Oct. 26, 1996, the disclosure of which is hereinincorporated by reference. In an alternative embodiment, the focusvalues determined by “whole way scanning” are used to set a rough focusposition, which is refined using a fine focus mode, as described incommonly assigned U.S. Pat. No. 5,715,483, entitled “Automatic FocusingApparatus and Method”, filed by Omata et al. on Oct. 11, 1998, thedisclosure of which is herein incorporated by reference.

Digital camera 12 has a rangefinder 27. Rangefinder 27 is adapted todetermine a distance from imaging system 20 to at least a portion of afield of view of taking lens system 23. Rangefinder 27 can determine thedistance as an absolute distance measurement, such as a measurement infeet or meters, or as a relative distance measurement to the focussetting for taking lens system 23 that is appropriate for the distanceto the subject without use of it. Rangefinder 27 can operate lens driver25, directly or as shown in FIG. 1, can provide signals to signalprocessor 26 or controller 32 from which signal processor 26 orcontroller 32 can generate signals that are to be used for imagecapture. A wide variety of suitable multiple sensor rangefinders 27known to those of skill in the art are suitable for use. For example,U.S. Pat. No. 5,440,369 entitled “Compact Camera With Automatic FocalLength Dependent Exposure Adjustments” filed by Tabata et al. on Nov.30, 1993, the disclosure of which is herein incorporated by reference,discloses one such rangefinder 27. The focus determination provided byrangefinder 27 can be of the single-spot or multi-spot type. Preferably,the focus determination uses multiple spots. In multi-spot focusdetermination, the scene is divided into a grid of areas or spots, andthe optimum focus distance is determined for each spot. One of the spotsis identified as the subject of the image and the focus distance forthat spot is used to set the focus of taking lens system 23.

A feedback loop is established between lens driver 25 and controller 32and/or rangefinder 27 so that the focus position of taking lens system23 can be rapidly set.

Taking lens system 23 is also optionally adjustable to provide avariable zoom. In the embodiment shown lens driver 25 automaticallyadjusts the position of one or more mobile elements (not shown) relativeto one or more stationary elements (not shown) of taking lens system 23based upon signals from signal processor 26, an automatic rangefinder27, and/or controller 32 to provide a zoom magnification. Taking lenssystem 23 can be of a fixed zoom setting, manually adjustable and/or canemploy other known arrangements for providing an adjustable zoom.

Light from the scene that is focused by taking lens system 23 onto sceneimage sensor 24 is converted into image signals representing an image ofthe scene. Scene image sensor 24 can comprise a charge couple device(CCD), a complimentary metal oxide sensor (CMOS), or any otherelectronic image sensor known to those of ordinary skill in the art. Theimage signals can be in digital or analog form.

Signal processor 26 receives image signals from scene image sensor 24and transforms the image signals into a digital image in the form ofdigital data. The image can comprise one or more still images, multiplestill images and/or a stream of apparently moving images such as a videosegment. Where the digital image data comprises a stream of apparentlymoving images, the digital image data can comprise image data stored inan interleaved or interlaced image form, a sequence of still images,and/or other forms known to those of skill in the art of digital video.

Signal processor 26 can apply various image processing algorithms to theimage signals when forming a digital image. These can include but arenot limited to color and exposure balancing, interpolation andcompression. Where the image signals are in the form of analog signals,signal processor 26 also converts these analog signals into a digitalform. In certain embodiments, signal processor 26 can be adapted toprocess image signals so that the digital image formed thereby appearsto have been captured at a different zoom setting than that actuallyprovided by the optical lens system. This can be done by using a subsetof the image signals from scene image sensor 24 and interpolating thesubset of the image signals to form the digital image. This is knowngenerally in the art as “digital zoom”. Such digital zoom can be used toprovide electronically controllable zoom adjusted in fixed focus, manualfocus, and even automatically adjustable focus systems.

Controller 32 controls the operation of the imaging system 10 duringimaging operations including, but not limited to, scene image capturedevice 22, display 30 and memory such as memory 40. Controller 32 causesscene image sensor 24, signal processor 26, display 30 and memory 40 tocapture, present and store scene images in response to signals receivedfrom a user input system 34, data from signal processor 26 and datareceived from optional sensors 36. Controller 32 can comprise amicroprocessor such as a programmable general purpose microprocessor, adedicated micro-processor or micro-controller, a combination of discretecomponents or any other system that can be used to control operation ofimaging system 10.

Controller 32 cooperates with a user input system 34 to allow imagingsystem 10 to interact with a user. User input system 34 can comprise anyform of transducer or other device capable of receiving an input from auser and converting this input into a form that can be used bycontroller 32 in operating imaging system 10. For example, user inputsystem 34 can comprise a touch screen input, a touch pad input, a 4-wayswitch, a 6-way switch, an 8-way switch, a stylus system, a trackballsystem, a joystick system, a voice recognition system, a gesturerecognition system or other such systems. In the digital camera 12embodiment of imaging system 10 shown in FIGS. 1 and 2 user input system34 includes a capture button 60 that sends a capture signal tocontroller 32 indicating a desire to capture an archival image. Userinput system 34 can also include other buttons including the joystick66, mode button 67, and the select it button 68 shown in FIG. 2.

Sensors 36 are optional and can include light sensors and other sensorsknown in the art that can be used to detect conditions in theenvironment surrounding imaging system 10 and to convert thisinformation into a form that can be used by controller 32 in governingoperation of imaging system 10. Sensors 36 can include audio sensorsadapted to capture sounds. Such audio sensors can be of conventionaldesign or can be capable of providing controllably focused audio capturesuch as the audio zoom system described in U.S. Pat. No. 4,862,278,entitled “Video Camera Microphone with Zoom Variable Acoustic Focus”,filed by Dann et al. on Oct. 14, 1986. Sensors 36 can also includebiometric sensors adapted to detect characteristics of a user forsecurity and affective imaging purposes. Sensors 36 can also includetemperature sensors or humidity sensors to detect the environmentalconditions surrounding the imaging system 10. Where a need foradditional scene illumination is determined, controller 32 can cause anoptional source of artificial illumination 37 such as a light, strobe,or flash system to emit light.

Controller 32 causes an image signal and corresponding digital image tobe formed when a capture condition is detected indicating a desire of auser to capture an archival image. Typically, the capture conditionoccurs when a user depresses capture button 60, however, controller 32can determine that a capture condition exists at a particular time, orat a particular time after capture button 60 is depressed.Alternatively, controller 32 can determine that a capture conditionexists when optional sensors 36 detect certain environmental conditions,such as optical or radio frequency signals. Further, controller 32 candetermine that a capture condition exists based upon affective signalsobtained from sensors 36 that are adapted to sense the physiology of auser.

Controller 32 can also be used to generate metadata in association witheach image. Metadata is data that is related to a digital image or aportion of a digital image but that is not necessarily observable in theimage itself. In this regard, controller 32 can receive signals fromsignal processor 26, camera user input system 34 and other sensors 36and, optionally, generate metadata based upon such signals. The metadatacan include, but is not limited to, information such as the time, dateand location that the scene image was captured, the type of scene imagesensor 24, mode setting information, integration time information,taking lens system 23 setting information that characterizes the processused to capture the scene image and processes, methods and algorithmsused by imaging system 10 to form the scene image. The metadata can alsoinclude but is not limited to any other information determined bycontroller 32 or stored in any memory in imaging system 10 such asinformation that identifies imaging system 10, and/or instructions forrendering or otherwise processing the digital image with which themetadata is associated. The metadata can also comprise an instruction toincorporate a particular message into a digital image when the digitalimage is presented. Such a message can be a text message that isintended to be shown or rendered when the digital image is presented orrendered. The metadata can also include audio signals. The metadata canfurther include digital image data. In one embodiment of the invention,where digital zoom is used to form the image from a subset of thecaptured image, the metadata can include image data from portions of animage that are not incorporated into the subset of the digital imagethat is used to form the digital image. The metadata can also includeany other information entered into imaging system 10, sensed by imagingsystem 10 or determined in whole or in part by imaging system 10.

A captured digital image and optional metadata, can be stored as anarchival image or used for other purposes as described herein. A digitalimage can be stored, for example, in a compressed form. For example,where the digital image comprises a sequence of still images, the stillimages can be stored in a compressed form such as by using the JPEG(Joint Photographic Experts Group) ISO 10918-1 (ITU-T.81) standard. ThisJPEG compressed image data is stored using the so-called “Exif” imageformat defined in the Exchangeable Image File Format version 2.2published by the Japan Electronics and Information Technology IndustriesAssociation JEITA CP-3451. Similarly, other compression systems such asthe MPEG-4 (Motion Pictures Export Group) or Apple QuickTime™ standardcan be used to store digital image data in a video form. Other imagecompression and storage forms can be used.

The digital images and metadata can be stored in a memory such as memory40. Memory 40 can include conventional memory devices including solidstate, magnetic, optical or other data storage devices. Memory 40 can befixed within imaging system 10 or it can be removable. In the embodimentof FIG. 1, imaging system 10 is shown having a memory card slot 46 thatholds a removable memory 48 such as a removable memory card and has aremovable memory interface 50 for communicating with removable memory48. The digital images and metadata can also be stored in a remotememory system 52 that is external to imaging system 10 such as apersonal computer, computer network or other imaging system.

In the embodiment shown in FIGS. 1 and 2, imaging system 10 has acommunication module 54 for communicating with external devices such as,for example, remote memory system 52. The communication module 54 can befor example, an optical, radio frequency or other wireless circuit ortransducer that converts image and other data into a form, such as anoptical signal, radio frequency signal or other form of signal, that canbe conveyed to an external device. Communication module 54 can also beused to receive a digital image and other information from a hostcomputer, network (not shown), or other digital image capture or imagestorage device. Controller 32 can also receive information andinstructions from signals received by communication module 54 includingbut not limited to, signals from a remote control device (not shown)such as a remote trigger button (not shown) and can operate imagingsystem 10 in accordance with such signals.

Signal processor 26 and/or controller 32 also use image signals or thedigital images to form evaluation images which have an appearance thatcorrespond to scene images stored in imaging system 10 and are adaptedfor presentation on display 30. This allows users of imaging system 10to use a display such as display 30 to view images that correspond toscene images that are available in imaging system 10. Such images caninclude images that have been captured by scene input capture deviceand/or that were otherwise obtained such as by way of communicationmodule 54 and stored in a memory such as memory 40 or removable memory48.

Display 30 can comprise, for example, a color liquid crystal display(LCD), organic light emitting display (OLED) also known as an organicelectro-luminescent display (OELD) or other type of video display.Display 30 can be external as is shown in FIG. 2, or it can be internalfor example used in a viewfinder system 38. Alternatively, imagingsystem 10 can have more than one display 30 with, for example, one beingexternal and one internal.

Signal processor 26 and/or controller 32 can also cooperate to generateother images such as text, graphics, icons and other information forpresentation on display 30. This can allow interactive communicationbetween controller 32 and a user of imaging system 10, with display 30providing information to the user of imaging system 10 and the user ofimaging system 10 using user input system 34 to interactively provideinformation to imaging system 10. Imaging system 10 can also have otherdisplays such as a segmented LCD or LED display (not shown) which canalso permit signal processor 26 and/or controller 32 to provideinformation to user. This capability is used for a variety of purposessuch as establishing modes of operation, entering control settings, userpreferences, and providing warnings and instructions to a user ofimaging system 10.

In the embodiments of FIGS. 1 and 2, imaging system 10 has an optionalaudio system 70 having an input transducer in the form of a microphone72 that receives sonic energy and generates signals that are provided toaudio processing circuitry 74. Audio processing circuitry 74 is adaptedto convert the signals received from microphone 72 into an electronicaudio signal representing the pattern of sonic energy incident upon thetransducer. Audio processing circuitry 74 is further adapted to receivesignals from controller 32 and to cause speaker 76 to generate audiblesounds. Other systems such as known circuits, lights and actuators forgenerating visual signals, audio signals, vibrations, haptic feedbackand other forms of signals can also be incorporated into imaging system10 for use in providing information, feedback and warnings to the userof imaging system 10.

Typically, display 30 has less imaging resolution than scene imagesensor 24. Accordingly, signal processor 26 reduces the resolution of acaptured or stored image signal or digital image when forming evaluationimages adapted for presentation on display 30. Down sampling and otherconventional techniques for reducing the overall imaging resolution canbe used. For example, resampling techniques such as are described incommonly assigned U.S. Pat. No. 5,164,831 “Electronic Still CameraProviding Multi-Format Storage Of Full And Reduced Resolution Images”filed by Kuchta et al. on Mar. 15, 1990, can be used. The evaluationimages can optionally be stored in a memory such as memory 40. Theevaluation images can be adapted to be provided to an optional displaydriver 28 that can be used to drive display 30. Alternatively, theevaluation images can be converted into signals that can be transmittedby signal processor 26 in a form that directly causes display 30 topresent the evaluation images. Where this is done, display driver 28 canbe omitted.

FIG. 4 shows a block diagram of a first method for auto-calibrating therangefinder based autofocus system in which a digital camera 12 isturned ON without an instruction to immediately capture an archivalimage. As is illustrated in FIG. 4, when controller 32 detects that auser has taken an action to activate digital camera 12 (step 80),controller 32 causes a calibration image 100 of a first field of view tobe automatically captured (step 82). FIG. 5 illustrates one example ofsuch a calibration image 100.

Controller 32 can determine a taking lens setting for use in capturingcalibration image 100 by setting lens system 23 to a predetermined firstfocus distance setting which can be for example a position at a middleof an adjustable range of taking lens system 23. However, in otherembodiments controller 32 can select any of the other focus distancesettings. Alternatively, controller 32 can be adapted to capture animage using whatever focus distance setting lens system 23 is set at themoment that controller 32 detects some condition indicating that digitalcamera 12 is to be activated.

Signal processor 26 and/or controller 32 portion the calibration image100 into portions 102-118 and identify one of the portions 102-118 ofcalibration images 100 as having a preferred level of focus as that termis understood in the art (step 84). Such focus level can, for example,be determined by examining any or all of the level of contrast, clarity,detail, distinctiveness or outline found in the image, or using anyother known metric for analyzing image focus. The preferred level offocus can be defined in relative terms by way of comparison with otherportions. In one specific example, where calibration image 100 is storedby compression in the frequency domain, portions of calibration image100 having higher degrees of focus can be located by identifyingportions in the stored image that have a greater amount of highfrequency data which in turn is indicative of the level of focus.

Typically the various portions 102-118 of calibration image 100 willdepict scene elements with greater and lesser degrees of focus and thuscontroller 32 or signal processor 26 will identify one area (e.g. area116) as having the greatest degree of focus. It will be appreciated thatin other embodiments, controller 32 can be adapted to simply identifythe first portion that has a level of focus that is above a thresholdand to select that portion. Other approaches can also be used.

Rangefinder 27 is used to measure a calibration focus distance from thedigital camera 12 to selected portion 116 using for example multi-spotrange finding to measure the distance from digital camera 12 to aportion of the field of view associated with the “spot” (step 86). Inone embodiment, controller 32 and/or signal processor 26 dividecalibration image 100 into portions that correspond directly to theportions associated with each “spot” used by rangefinder 27. However,this is not strictly necessary so long as there exists a generalcorrespondence between the size and location of the identified portion116 and the portion of the field of view used by rangefinder 27 inmeasuring the distance to the designated portion to measure a distanceto that portion.

In one embodiment, calibration image 100 is captured at about the sametime that rangefinding measurements are made for portions of the fieldof view associated with each rangefinding “spot” in the scene. Thisreduces the likelihood that the composition of the scene can changebetween the time of image capture and the time of rangefindingmeasurements. However, it will be appreciated that minor time variationswill be acceptable in certain applications.

A focus correlation is then determined based upon the calibrationdistance and the focus distance setting used to capture the calibrationimage (step 88). The focus correlation can be any type of data,programmic, algorithmic, mathematical or logical structure thatassociates different rangefinder distance values with different focussettings for lens system 23. FIG. 6 shows one example of a focuscorrelation expressed, in this example, in the form of a two-dimensionallook-up table (LUT). In this example, taking lens system 23 can be setinto one of ten focus distance settings focusing light from a differentrange of distances onto scene image sensor 24 associated with a range offocus distances. Each of the ten focus distance settings is alsoassociated with a rangefinding distance. In a typical camera of theprior art this correlation set is fixed for all images. However, asnoted above, such an arrangement does not permit digital camera 12 toadjust to variations in operation due to environmental conditions ormechanical variations.

Accordingly, in this embodiment, digital camera 12 has a plurality offocus correlations available. For this example, controller 32 can selectfrom two other focus correlation LUTs. This plurality is depicted hereinas three different LUTs in FIGS. 6, 7 and 8. Controller 32 selects fromamong the available LUTs by looking for the focus correlation thatprovides a combination of focus setting and a capture focus distancethat most closely correlates to the focus setting used to capture thecalibration image and the calibration focus distance determined byrangefinder 27 for the portion of the image identified as having thepredetermined degree of focus at that focus setting. For example, iftaking lens system 23 was focused at setting 3 during capture of thecalibration image and the determined focus calibration distance was 0.6meters, then controller 32 would select the focus correlation depictedin FIG. 8.

In other embodiments, the focus correlation can take other forms and canbe expressed, for example, in the form of a mathematical expression suchas linear, binomial polynomial or other mathematical function. Insimilar fashion, controller 32 can select from among the mathematicalexpressions the one for which the focus setting and measuredrangefinding distance best correlate. As is noted generally above instill other embodiments, the plurality of focus correlations can takethe form of different programmic, algorithmic or logic structuresincluding, but not limited to, a plurality of different fuzzy logicstructures. Three dimensional LUTs can also be used.

Data is then stored in memory 40 in the form that indicates which of thedetermined focus correlations is to be used for future image captureoperations (step 90). This storage process can also involve recordingthe time and date and or any other sensed conditions that may influencethe selected focus correlation. This allows controller 32 to determine,at a later time, whether there exists a need to verify that thedetermined focus correlation is still valid. Further, where digitalcamera 12 has sensors 36 that are adapted to sense conditions such ashumidity sensors of any type known in the art, temperature sensors ofany type known in the art or any other sensors of conditions that mightinfluence the operation of lens system 23, controller 32 can store datawith the indication of the determined focus correlation that indicatesthe state of these conditions at the time of determining the focuscorrelation. In another embodiment where digital camera 12 hasselectable scene modes for capturing particular types of images, such aslandscape modes, portrait modes, close up modes and the like, the scenemode used during calibration can be stored with the indication.

In this embodiment, controller 32 is programmed or otherwise adapted sothat when controller 32 detects a capture condition indicating that anarchival image is to be captured (step 92), such as a user depression ofcapture button 60, controller 32 co-operates with rangefinder 27 tomeasure the distance from digital camera 12 to portions of the scenethat are then determined to be within the field of view of taking lenssystem 23, and measures distances from digital camera 12 to a pluralityof portions within the field of view, selects one of the portions as thesubject of the image and uses the distance from digital camera 12 to theselected portion as a capture focus distance (step 94). Controller 32then applies the capture focus distance to the determined focuscorrelation to determine a focus distance setting for image capturesystem 22 and captures the subsequent archival image (step 96). If morearchival images are to be captured, the process returns to step 92, ifnot the process ends (step 98).

FIG. 9 shows still another embodiment of a method for calibrating animaging device which can be applied to help a digital camera 12 undercircumstances where the user evidences a desire to immediately capturean archival image upon activation of the camera. This may occur, forexample, where the user indicates a desire to capture an imageimmediately upon activation of digital camera 12. Under suchcircumstances, a user may not be willing to wait for the camera toexecute the calibration process described above with respect to FIGS.4-9 before capturing the image. Accordingly, in this embodiment, whencontroller 32 detects that digital camera 12 has been activated (step120) and that a capture condition exists, such as may be caused by adepression of the capture button 60 (step 122), controller 32 uses athrough-the-lens focus technique as described above in order todetermine a setting for taking lens system 23 that causes at least asubject area portion of the field of view captured by taking lens system23 to be in focus (step 124) and to capture an archival image at thatfocus setting (step 126).

At about the same time, rangefinder 27 determines a capture focusdistance from digital camera 12 to the subject area portion of the fieldof view captured by taking lens system 23 (step 128). This can involvewaiting until “through-the-lens” autofocusing has identified a portionas the subject area and then measuring the distance from digital camera12 to that portion, or it can involve measuring the distance fromrangefinder 27 to any portions within the field of view and thenchoosing the distance between rangefinder 27 and a portion thatcorresponds to the subject area as a calibration rangefinding distance.

A focus correlation is then determined based upon the calibrationdistance and the focus distance setting used to capture the archivalimage which in this case also comprises a calibration image (step 130)as described above. Data is then stored in memory 40 in the form of aplurality of focus correlations to be used for future image captureoperations (step 132).

In this embodiment, when controller 32 determines that capture button 60has been pushed again or otherwise determines that it is necessary tocapture a second image (step 134), controller 32 then uses rangefinder27 to determine a capture focus distance (step 136) and then uses thecapture focus distance and the determined focus correlation to select afocus setting for taking lens system 23 for use in capturing asubsequent image (step 138). Where more images are to be captured (step140), the process can return to step 134.

It will be appreciated that in order to ensure optimum focus distancesetting performance, it may be necessary to verify that a previouslydetermined focus correlation remains valid. In the embodiment of FIG.10, this is performed by adding a verification process (steps 91 and 93)within the method discussed above with respect to FIG. 4. In the exampleshown in FIG. 10, controller 32 can be adapted to determine that thereis a reasonable possibility that camera operating conditions havechanged since the last time that a focus correlation was determined(step 91). For example, where the step of storing an indication (step90) includes storing date and time information indicating the date andtime at which a focus correlation was last determined, controller 32 canuse this information to determine whether so much time has elapsed sincethe last determination that it is necessary to do another calibration.If too much time has passed then the process returns to step 82 (step93). A similar result can be obtained where scene mode information isstored with the indication.

A similar approach applies when temperature or other conditions arestored with the indication, in that if there has been a temperature orhumidity change or a change in any other sensed conditions in whichdigital camera 12 is used, controller 32 can return the process to step82. In an alternative not shown, the process can be returned to step 122so that an archival image can be quickly captured with recalibrationperformed thereafter.

Where analysis of the calibration start condition does not suggest thatthere is a need for calibration (step 93) the process simply continuesto allow image capture of a subsequent image using the previouslydetermined image capture process.

An optional verification process (step 97) is also illustrated in FIG.10 and can be performed with or without the optional step of sensing fora calibration start condition. In the verification process, therangefinder 27 is used to sense a capture distance to a subject areawithin the field of view of lens system 23. The capture distance is thenapplied to the previously indicated focus correlation to determine atwo-lens focus setting. Taking lens system 23 is then set to theindicated lens setting and an image is captured. Controller 32 and/orsignal processor 26 then determines whether the portion of the capturedimage has a predetermined degree of focus. Where it is determined thatcontroller 32 does not have the predetermined degree of focus in thesubject area, controller 32 can return to step 82 for recalibration. Inan alternative embodiment not shown, controller 32 can return to step 84and can recalibrate by selecting a focus correlation using the lastarchival image and rangefinding data associated with the last archivalimage using the method described above in FIG. 10.

FIG. 11 shows an alternative embodiment of a method for calibrating animaging device 10, useful at least in a second scenario forauto-calibrating the rangefinder based autofocus system in which theuser activates digital camera 12 (step 150) and immediately pushescapture button 60, or otherwise causes a capture condition to begenerated (step 152). In this second case, rangefinder 27 measures thedistance from digital camera 12 to a subject area portion in the fieldof view (step 154) and selects a preprogrammed focus correlation. Theselected focus correlation and the measured distance is then used forarchival image capture (step 158). At the first available opportunity, afocus correlation is determined (step 160) and an indication of thedetermined focus correlation is stored (step 162). Subsequent archivalimages can then be captured using rangefinder 27 and determined focuscorrelation (steps 164-170). The data for the measured distance and thecalibration curve are then stored in memory 40 for later reference.

FIG. 12 shows a block diagram of yet another embodiment of a calibrationmethod in which digital camera 12 is activated (step 180) and capturebutton 60 is pushed by the camera operator to indicate an immediatedesire to capture an image (step 182). In response, controller 32 thendetects an operating condition, such as a temperature, humidity, time ofcapture, scene type or other capture condition (step 184) and selects afocus correlation based upon the detected operating conditions. Forexample, controller 32 can cause a sensor 36 to measure the temperatureof digital camera 12 and/or the environment around digital camera 12(step 184). Controller 34 selects one of a set of focus correlationsthat are associated with a measured temperature range (step 186). FIGS.13-15 illustrate for example, focus correlations in the form ofthree-dimensional LUTS, with each LUT being associated with a differentrange of temperatures.

Controller 32 then uses rangefinder 27 to measure a capture distancefrom digital camera 12 to the subject area portion of the field of viewof taking lens system 23 (step 188) and captures an archival image withtaking lens system 23 set to a focus distance that is selected basedupon the focus correlation and the rangefinder measured capture distance(step 190).

At the first available opportunity, a through-the-lens method is used todetermine a focus setting (step 192) for a calibration image, this isused to determine a focus correlation (step 194) and an indication ofthe determined focus correlation is stored (step 196). Subsequentarchival images can then be captured using rangefinder 27 to measurecaptured distance and the determined focus correlation to determine lensfocus distances for use in image capture (steps 198-204).

FIG. 16 shows an alternative embodiment of a method for determining afocus correlation that can be used for example in any of steps 88, 130,164, or 194. In this embodiment, controller 32 first examines whetherany existing focus correlation fits with the measured rangefindingdistance and the focus distance setting used to capture a calibrationimage or archival image (step 210). If so, the fitting focus correlationis used and the process ends (step 212). If not, controller 32 evaluatesthe calibration image to identify at least one portion of thecalibration image having a focus that is at or above the predeterminedfocus level (step 214). Rangefinder 27 is then used to measure adistance to the portions of the calibration image that are in focus withtaking lens system 23 at the focus distance setting used to capture thecalibration image (step 216). The measured range of distances is thenassociated with the focus distance setting used to capture thecalibration image and forms a portion of a focus correlation (step 218).

If a calibration image has not yet been captured at each of a pluralityof focus distance settings representing the range of focus distancesettings that taking lens system 23 can be moved into (step 220) thentaking lens system 23 is moved to a different focus distance setting(step 222) and an additional calibration image is captured (step 224).Steps 214-220 are repeated until a calibration image has been capturedat each of a plurality of focus distance settings representing the rangeof focus distance settings that taking lens system 23 can be moved intoand steps 214-220 have been performed on all of these images. A focuscorrelation is then determined using the data associations obtainedduring the performance of steps 214-220 (step 226) and the processreturns to the steps described above.

In one embodiment this is done simply by associating each of the focusdistance positions with the range of distances measured when that focusdistance was used. In other embodiments interpolation and/or regressiontechniques can be used to define a range of focus distance measurementwith each focus distance setting to form the focus correlation.Alternatively, an existing focus correlation can be adjusted todetermine focus correlation based upon the measured information.

FIG. 17 shows a block diagram of another embodiment wherein imagingsystem 10 is operably associated with a digital video image projectionsystem 300 and FIG. 18 shows a method for using imaging system 10 tohelp improve image quality of an image projected by projection system300. This can be done for example, by physically linking the projectionsystem 300 to imaging system 10 such as by way of a wired or opticalconnection or by way of a wireless connection.

Where such an arrangement is provided, imaging system 10 can interactwith projection system 300 to provide improved quality projected images.For example, FIG. 18 shows a block diagram of an embodiment in whichimaging system 10 is used to calibrate a projection system 300.Projection system 300 can be mounted to body 20 or it can be separatetherefrom with a physical connection therebetween, such as a wiredconnection or other logical connection therebetween, such as a wirelessconnection.

Projection system 300 receives a digital image and projects the imageonto an available wall or other available surface (step 310). It will beappreciated that the appearance of a projected image formed thereon is aproduct of a combination of the received image, the projection systemand color, light and reflection characteristics of the available wall orother available projection surface. In particular, the surface that theimage is being projected on is often not an ideal white surface, such asoften occurs when the projector is used in a home environment orbusiness travel environment or in spontaneous sharing moments when aprojection screen is not available, instead the surface often has it'sown color or multiple colors or shadows or even a texture. In this caseit would be beneficial to the projected image quality if the image couldbe adjusted to calibrate for the characteristics of the surface that theimage is to be projected onto. Further, in some cases, it may bedesirable, or necessary, to project the image against a surface havingmeaningful topographical variations such that might impact a focusdistance. Accordingly, compensation for these factors is preferred.

To provide such compensation, controller 32 causes an image to becaptured of the projected image (step 312) with taking lens system 23set so that the captured image encompasses at least a portion of theprojected image. The captured image of the projected image is thencompared to the corresponding portion of the original image bycontroller 32 and/or signal processor 26 to form a difference map (step314). The difference map reflects differences between the appearance ofthe received image and the appearance of the image as a function of theprojection system and the color, light and reflection characteristics ofthe available wall or other available surface. The difference map isthen provided for use by imaging system 10 or projection system 300 inadjusting the projected image by recalibrating the digital projector forthe projection system and the color or colors of the wall or any shadowson the wall or any texture that is present on the available wall orother available surface (step 316).

Measuring data from rangefinder 27 can also be obtained (step 318) andused as a part of this process first to calibrate imaging system 10 asdescribed above and also to be used to detect any variations in theshape, depth, or orientation of the projection surface which may not bereadily apparent from the image captured by the scene image capturesystem 22 (step 320). Signal processor 26 and/or controller 32 can usethe detected distance information to determine possible modifications tothe difference map or other signals that are provided for use inmodified images presented by projection system 300 (step 322).Alternatively, controller 32 can generate focus adjustments for use byprojection system 300. In particular, controller 32 can be adapted touse determined rangefinder distances for various portions of a surfaceonto which an image is projected and can cause focus setting adjustmentsto be made. In one embodiment of the imaging system 10 illustrated inFIG. 16, it is contemplated that imaging system 10 will comprise aprojection system 300 that is not permanently connected to body 20 andthat can be connected thereto, as desired, during periods ofcooperation. It will be appreciated that in such an embodiment,calibration of projection system 300 becomes possible using structuresprovided by the digital camera 12 so that the calibration benefitsdescribed herein can be obtained without incorporating such structuresinto projection system 300.

In this embodiment, it is important to note that the calibration may beperformed for each setup of the projection system 300 or for eachprojected image individually. In the case where the calibration isperformed for each projected image individually, a new difference map isformed for each projected image individually. In the case where thecalibration is performed for each setup, a difference map is formed forthe first projected image and then the same difference map is applied toeach subsequent projected image.

In a further embodiment, will be appreciated that scene image sensor 24has a plurality of image sensing positions each having a gain. The gainat each image sensing pixel can vary from pixel to pixel. Accordingly,another aspect of imaging system 10 that could benefit from calibrationis calibration of the image capture system 22 when using a multi-channeltype image sensor 24. In the case of a multi-channel type image sensor24, the response of the image to light from the scene is typicallyslightly different between channels. Minor variations during fabricationof the image sensors cause differences in the electrical characteristicsof the channels and slightly different gain, typically on the order of1%. These differences in channel response result in abrupt changes inthe image along the corresponding lines where the channels abut oneanother on the image sensor. In addition, the differences betweenchannels change over time and as the environmental conditions such astemperature and humidity change.

If these gain variations are not compensated for, they can introducenoise in captured digital images. Accordingly, a calibration method isneeded which can enable compensation of the channel differences to becompensated to improve image quality. What is also needed is acalibration method that can react to changes in channel differences overtime and as environmental conditions such as temperature and humiditychange.

To filter such effects from captured images, controller 32 can capturean image with low contrast which can be used to calibrate the gain ofimage capture pixels or the channels for a multi-channel image sensor24. To achieve this, a position of extreme defocus is identified by theautofocus system in which the image has low contrast. The low contrastimage is then used by the signal processor 26 to set the gains oroffsets for the different pixels and channels of the image sensor 24 tocompensate for the differences in electrical characteristics present onthe multiple channels of the image sensor 24. In this context, it isworth noting the low contrast is relative to the spatial frequencyassociated with the pixels between channels.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   10 imaging system-   12 digital camera-   20 body-   22 scene image capture system-   23 taking lens system-   24 scene image sensor-   25 lens driver-   26 signal processor-   27 automatic rangefinder-   28 display driver-   30 display-   32 controller-   34 user input system-   36 sensors-   37 artificial illumination source-   38 viewfinder-   40 memory-   46 memory card slot-   48 removable memory-   50 removable memory interface-   52 remote memory system-   54 communication module-   60 capture button-   66 joystick-   67 mode button-   68 select-it button-   70 audio system-   72 microphone-   74 audio processing circuitry-   76 speaker-   80 activate camera step-   82 capture calibration image step-   84 identify portion of calibration image that has preferred level of    focus step-   86 measure calibration distance from image capture system to    identified portion step-   88 determine focus correlation step-   90 store indication step-   91 detect operating conditions step-   92 capture condition detected step-   93 operating conditions changed step-   94 detect capture distance step-   96 capture image and capture distance to determine focus setting    step-   97 verify focus in subject portion of image step-   98 more images determine step-   100 calibration image-   102 portion of calibration image-   104 portion of calibration image-   106 portion of calibration image-   108 portion of calibration image-   110 portion of calibration image-   112 portion of calibration image-   114 portion of calibration image-   116 portion of calibration image-   118 portion of calibration image-   120 camera activated step-   122 detect capture depression step-   124 use through-the-lens focus technique to determine focus distance    setting step-   126 capture archival image step-   128 determine capture focus distance from camera to subject area of    field of view captured step-   130 focus correlation determined step-   132 stored data to be used for future image capture operations step-   134 determination to capture a second image step-   136 determine capture focus distance step-   138 select focus setting for use in capturing subsequent image step-   140 capture more images step-   150 activate camera step-   152 capture button pushed step-   154 measure distance from image capture system to subject area    portion step-   156 use pre-programmed focus correlation to determine focus distance    step-   158 capture archival image step-   160 determine a focus correlation and the focus distance used to    capture archival image step-   162 store indication of determined focus correlation step-   164 capture condition detected step-   166 detect capture distance step-   168 capture image and capture distance to determine focus setting    step-   170 more images determining step-   180 activate camera step-   182 capture button pushed step-   184 detect operating conditions step-   186 select focus correlation based upon operating conditions step-   188 measure distance from capture system to subject area portion    step-   190 capture archival image step-   192 use through-the-lens focus to determine settings for capturing    archival image step-   194 determine a focus correlation step-   196 store correlation step-   198 detect capture condition step-   200 detect capture distance step-   202 capture image step-   204 more images determining step-   210 does measured information fit known focus correlation-   212 select fitting focus correlation-   214 identify portion of calibration image having focus above    predetermined focus level-   216 measure distance step-   218 determine and associate range of distances step-   220 more focus positions step-   222 move lens system to capture a calibration image step-   224 capture additional calibration image step-   226 determine focus correlation step-   300 projection system-   310 project image step-   312 capture image of projected image step-   314 calculate difference map step-   316 store difference map for use step-   317 adjust projected image step based on difference map-   318 determine rangefinding distances step-   320 detect variations in rangefinding distances step-   322 determine image adjustments based upon rangefinding distances    step-   323 adjust projected image step based on rangefinding distances

1. A method for calibrating an imaging system having mounted to a body,a scene image capture system that captures images using a taking lenssystem that can be set to a plurality of different focus distances and arangefinder that is capable of determining a distance between theimaging system and at least one portion of a field of view of the takinglens system, without using the image capture system, the methodcomprising the steps of: automatically capturing a first calibrationimage of a first field of view through the taking lens system with thetaking lens system set to a first focus distance setting; identifying aportion of the first calibration image having a predetermined degree offocus; using the rangefinder to determine a first calibration distancefrom the imaging device to the identified portion of the firstcalibration image; determining a focus correlation based upon the firstcalibration distance and the first focus distance setting, said focuscorrelation associating each of the plurality of focus distance settingswith at least one rangefinder determined distance; and detecting acapture condition indicating that the scene image capture system is tobe used to capture an archival image of a scene, and in responsethereto, performing the steps of: determining a capture distance fromthe imaging system to a portion of the field of view of the taking lenssystem using the rangefinder, and setting the focus distance setting forthe taking lens system for the capture of the archival image based uponthe determined focus correlation and the determined capture distance. 2.The method of claim 1, further comprising the steps of: capturing asecond calibration image with the taking lens system focused at a secondfocus distance setting that is different from the first focus distancesetting and that depicts a portion of a second field of view having apredetermined degree of focus; and using the rangefinder to measure asecond calibration distance from the imaging system to the portion ofthe field of view depicted in the second image having the predetermineddegree of focus; wherein the step of determining a focus correlationcomprises determining the focus correlation based upon the firstcalibration distance, the first focus distance setting, the secondcalibration distance, and the second focus distance setting.
 3. Themethod of claim 1, wherein said focus correlation comprises any of atwo-dimensional look up table, a three-dimensional look up table, abinomial, a polynomial, a fuzzy logic structure or an algorithm.
 4. Themethod of claim 1, wherein said step of determining a focus correlationcomprises selecting from among a predetermined number of different focuscorrelations.
 5. The method of claim 1, wherein said step of determininga focus correlation comprises adjusting mathematical or other logicalmodels of the relationship between different rangefinder determineddistance values and the plurality of focus settings.
 6. The method ofclaim 1, wherein said steps of capturing, identifying, using, anddetermining a focus correlation are performed automatically when it isdetected that there is a reasonable possibility that camera operatingconditions have changed since a last calibration, such camera operatingcondition comprising any of time change, a change in scene mode, achange in temperature or a change in humidity.
 7. The method of claim 1,further comprising the step of determining when there is insufficienttime to capture a calibration image before capturing an archival imageand, in response thereto, selecting a preliminary focus correlationusing a predetermined focus correlation using the rangefinding distanceand lens settings used to capture the archival image, using athrough-the-lens focusing technique, or using sensed conditions.
 8. Themethod of claim 1, further comprising the steps of: defocusing the lenssystem to obtain a low contrast image; identifying areas of differentcontrast; and adjusting gains for particular portions of an image sensorin the scene image capture system to provide even contrast.
 9. Themethod of claim 1, further comprising the steps of: receiving a digitalimage; causing a digital image projection system to project the obtaineddigital image onto a surface; capturing an image of the projected image;determining a difference map by comparison of the digital image and thecaptured image of the projected image; and using the difference map toalter the projected image to reduce the extent to which conditions onthe surface induce artifacts in the appearance of the projected image sothat the projected image has an appearance that more closely simulatesthe appearance of the received digital image.
 10. The method of claim 9,further comprising the steps of: obtaining rangefinding information forthe surface; and using the rangefinding information to adjust theprojection of the received image.
 11. The method of claim 9, wherein thedifference map is obtained for each surface that is projected on; andthe difference map is used as a calibration for the digital imageprojection system.
 12. The method of claim 9, wherein the difference mapis obtained for each projected image; and the difference map is used asa calibration for the digital image projection system.
 13. A method forcalibrating a scene image capture system having a taking lens systemthat focuses light from a field of view onto an image sensor and thatcan be set to a range of different focus settings to provide differentfocus distances said image capture system being mounted to a common bodywith a rangefinder that determines distances from the scene imagecapture system to portions of a scene within the field of view withoutusing the scene image capture system, the method comprising the stepsof: capturing a set of images with the taking lens system automaticallyset to a range of different focus settings for each image; andidentifying captured images that were captured with the lens system atdifferent settings than others of the captured images and that depict aportion of the field of view in focus, and obtaining for each identifiedimage a rangefinder determined distance from the scene image capturesystem to the portion of the field of view depicted in the identifiedimage that has a predetermined degree of focus; and storing correlationdata that associates the rangefinder determined distance for the imageand setting of the taking lens system at the time that the additionalimage was captured, so that a focus correlation can be establishedassociating distance values with corresponding focus settings over therange of different focus settings.
 14. The method of claim 13, furthercomprising the step of detecting a scene mode for capturing an image andwherein the steps of capturing, identifying, using, and storing areperformed with more focus correlation data being obtained for distancesthat are within a first range that are obtained for a second similardistance range, wherein the first distance range and the second distancerange are determined based upon a detected user input action, or cameraoperating condition.
 15. An imaging system comprising a body, a sceneimage capture system mounted to the body, said scene image capturesystem capturing images using a taking lens system that can be set to aplurality of different focus distances; a rangefinder mounted to thebody, said rangefinder being adapted to determine a distance between therangefinder and a portion of a scene within a field of view of the sceneimage capture system; and a controller adapted to automatically capturea first calibration image through the taking lens system with the takinglens system set to a first focus distance setting, to identify a portionof the first calibration image having a predetermined degree of focusand to use the rangefinder to measure a first calibration distance fromthe imaging device to the identified portion; wherein said controllerdetermines a focus correlation based upon the first calibration distanceand the first focus distance setting used to capture the first image,said focus correlation associating different rangefinder determineddistances with the plurality of focus distance settings; said controllerfurther being adapted to detect a capture condition indicating that theimage capture system is to be used to capture an archival image of ascene, and, when the capture condition is detected, the controllercauses the rangefinder to determine a capture distance from the imagingsystem to a portion of the field of view of the taking lens system, andthe focus distance setting for the taking lens system is set for thecapture of the image based upon the determined focus correlation and thedetermined capture distance.
 16. The imaging system of claim 15, whereinsaid controller is further adapted to capture a second calibration imagewith the lens system focused at a second focus distance setting that isdifferent from the first focus distance setting and that depicts aportion of the field of view having a predetermined degree of focus;uses the rangefinder to measure a second calibration distance from theimaging system to the portion of the field of view depicted in thesecond image that has the predetermined degree of focus; wherein thecontroller determines a focus correlation by determining the focuscorrelation based upon the first calibration distance, the first focusdistance setting, the second calibration distance, and the second focusdistance setting.
 17. The imaging system of claim 15, further comprisinga projection system adapted to receive a digital image and to cause thedigital image to be projected onto a surface, said controller furtherbeing adapted to obtain rangefinding information for the surface and toadapt a focus setting of the projection system based upon therangefinding information.
 18. The imaging system of claim 17, whereinthe controller is further adapted to cause the scene image capturesystem to capture a calibration image of the projected image and toadapt the focus setting of the projection system based upon the captureimage and the appearance of the projected image.
 19. The imaging systemof claim 15, wherein said controller causes said scene image capturesystem to capture a calibration image of the projected image and todetermine a difference map representing differences between the obtaineddigital image and the projected image, wherein said difference map isused to adjust the projected image so that the appearance of theprojected image more closely approximates the appearance of the receiveddigital image.
 20. The imaging system of claim 15, wherein saidprojection system is connected to the body and, wherein said projectionsystem is connected thereto by way of an interface during periods ofcooperation.